1. Field of the Invention
The present invention relates to an electric bicycle, and more particularly to a power transmission and pedal force sensing system for an electric bicycle.
2. Description of the Related Art
A conventional electric bicycle generally comprises a high speed electric motor used as an auxiliary power source, a gear reduction mechanism for reducing speed of the motor and increasing the output torque, and a power combining mechanism for combining the power from the motor after speed reduction and the pedaling power from the cyclist for subsequent transmission to a chain wheel for driving the electric bicycle at a labor-saving mode. A pedal force sensor is provided on a pedal force transmission path to detect the magnitude of the pedal force to thereby control auxiliary output power from the electric motor.
A transmission mechanism for the above conventional electric bicycle includes a frame mounted adjacent to a crankshaft of a bicycle and including a main casing and an auxiliary casing arranged in a direction perpendicular to the main casing. The power combining mechanism and the pedal force sensing mechanism are mounted in the main casing, while the electric motor and the gear reduction mechanism are mounted in the auxiliary casing. Bevel gears are used for transmission. Such a transmission mechanism has a low transmission efficiency as there are too many stages for gear reduction and the transmission path is too long. In addition, the electric motor is not mounted inside the main casing such that additional supporting casing and transmission elements are required, and this results in a bulky structure. Further, the sensing system adopts a bolt and nut or plane cam to convert relative angular displacement into axial displacement, which, in turn, is detected by a proximity sensor for outputting a signal corresponding to a magnitude of the pedal force. Yet, the elements of the pedal sensing system are located on the pedal force transmission path and are thus liable to wear.
The present invention is intended to provide a power transmission and pedal force sensing system that mitigates and/or obviates the drawbacks of the above conventional electric bicycle.